PNP 2025-047, Palisades Nuclear Plant - Response to Request for Additional Information Regarding License Amendment Request to Include Leak Before Break Methodology for Primary Coolant System Hot and Cold Leg Piping in Palisades Licensing Basis
| ML25191A022 | |
| Person / Time | |
|---|---|
| Site: | Palisades  |
| Issue date: | 07/10/2025 |
| From: | Fleming J Entergy Nuclear Operations, Holtec Palisades |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| PNP 2025-047 | |
| Download: ML25191A022 (1) | |
Text
27780 Blue Star Highway, Covert, MI 49043 1 Holtec Palisades, LLC ("Holtec Palisades") is the licensed owner of PNP. Holtec Decommissioning International, LLC ("HDI") is the licensed operator of PNP while the facility is in decommissioning. Pursuant to the license transfer application submitted in connection with the PNP restart (Reference 3), licensed authority will transfer from HDI to Palisades Energy, LLC ("Palisades Energy") upon NRC's approval of the transition from decommissioning back to power operations. Holtec Palisades will remain the licensed owner of PNP.
PNP 2025-047 10 CFR 50.90 July 10, 2025 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001 Palisades Nuclear Plant NRC Docket No. 50-255 Renewed Facility Operating License No. DPR-20
Subject:
Response to Request for Additional Information Regarding License Amendment Request to Include Leak Before Break Methodology for Primary Coolant System Hot and Cold Leg Piping in Palisades Licensing Basis By \
letter dated February 5, 2025 (Reference 1), as supplemented by \
letter dated February 27, 2025 (Reference 2), Holtec1 requested U.S. Nuclear Regulatory Commission (NRC) review and approval of a license amendment request (LAR) to revise the Palisades Nuclear Plant (PNP) licensing basis to include Leak Before Break (LBB) methodology for Primary Coolant System (PCS) hot and cold leg loop piping.
By electronic mail (email) received on May 20, 2025, the NRC forwarded a draft request for additional information (RAI) regarding the LAR. A clarification call with the NRC reviewers was held on June 9, 2025, to discuss the LAR, and the NRC provided the final RAI in an email dated June 10, 2025 (Reference 4). to this letter provides PNP responses to the RAI questions.
In accordance with 10 CFR 50.91(b), State consultation, Holtec is notifying the State of Michigan of these RAI responses by transmitting a copy of this letter, with Enclosure, to the designated State of Michigan official.
If you have any questions regarding this submittal, please contact Frank Sienczak, Regulatory Assurance Manager, at (269) 764-2263.
This letter contains no new regulatory commitments and no revisions to existing regulatory commitments.
I declare under penalty of perjury that the foregoing is true and correct. Executed on July 10, 2025.
PNP 2025-047 Page 2 of 2 Respectfully, Jean A. Fleming Vice President, Licensing and Regulatory Assurance Holtec International
==References:
==
1.
Holtec Palisades, LLC (Holtec) letter to U.S. Nuclear Regulatory Commission (NRC), License Amendment Request to Include Leak Before Break Methodology for Primary Coolant System Hot and Cold Leg Piping in Palisades Licensing Basis, dated February 5, 2025 (ADAMS Accession No. ML25035A216) 2.
Holtec Palisades, LLC (Holtec) letter to U.S. Nuclear Regulatory Commission (NRC), Supplement to License Amendment Request to Include Leak Before Break Methodology for Primary Coolant System Hot and Cold Leg Piping in Palisades Licensing Basis, dated February 27, 2025 (ADAMS Accession No. ML25058A265)
- 3.
Holtec Decommissioning International, LLC (HDI) letter to NRC, Application for Order Consenting to Transfer of Control of License and Approving Conforming License Amendments, dated December 6, 2023 (ADAMS Accession No. ML23340A161) 4.
NRC letter to Holtec, Request for Additional Information RE: Leak-Before-Break Amendment (L-2025-LLA-0027), dated June 10, 2025 (ADAMS Accession No. ML25161A218) : Response to Request for Additional Information - License Amendment Request to Include Leak Before Break Methodology for Primary Coolant System Hot and Cold Leg Piping in Palisades Licensing Basis cc:
NRC Region III Regional Administrator NRC Senior Resident Inspector - Palisades Nuclear Plant NRC Project Manager - Palisades Nuclear Plant Designated Michigan State Official Digitally signed by Jean A. Fleming DN: cn=Jean A. Fleming, o=Holtec Decommissioning International, LLC, ou=Regulatory and Environmental Affairs, email=J.Fleming@Holtec.com Date: 2025.07.10 07:29:45 -04'00' Jean A.
Fleming
PNP 2025-047 Page 1 of 6 PNP 2025-047 Response to Request for Additional Information License Amendment Request to Include Leak Before Break Methodology for Primary Coolant System Hot and Cold Leg Piping in Palisades Licensing Basis
PNP 2025-047 Page 2 of 6 Response to Request for Additional Information Question 1 Demonstrate that the Technical Specification (TS) listed components (TS 3.4.15 instrumentations b, c, and d) can detect a leakage rate of 1 gpm within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> as stated in Regulatory Guide (RG) 1.45, Revision 1, Regulatory Position (RP) 2.2, as a way to be in compliance with 10 CFR App A GDC 30.
Holtec Response to Question 1 PNP does not believe there is a regulatory requirement to demonstrate that all the TS 3.4.15 instrumentations a, b, c and d components can detect a leakage rate of 1 gpm within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />.
RG 1.45, Revision 1 (Reference 1), RP 2.2 does not state that all leakage detection systems used by the plant should be identified in TS.
RP 2.3 recommends plant TS should identify at least two independent and diverse instruments and/or methods that have the detection and monitoring capabilities detailed in RP 2.2. PNP discussion of RP 2.3 identified two such methods: containment sump level (TS 3.4.15a) and Primary Coolant System (PCS) water inventory balance (TS Surveillance Requirement (SR) 3.4.13.1).
Page 7 of RG 1.45, Revision 1, Section B., DISCUSSION, subsection, Monitoring System Performance, suggests all monitoring systems referenced in the TS should respond to a leakage increase of 1 gal/min (GPM) in 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> or less with respect to detector response times.
However, this suggestion is not carried forward when the RG provides RPs.
Page 10 of RG 1.45, Revision 1, RP 2.3 recommends Plant TS should identify at least two independent and diverse instruments and/or methods that have the detection and monitoring capabilities detailed above, where above refers to RP 2.2.
PNP LAR discussion for RP 2.2 in the LAR references the PNP RP 2.1 response which identifies that PNP has three systems which meet the 1 gpm in 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> requirement:
- 1) Containment sump level with a 0.01 gpm resolution,
- 2) PCS Water Inventory Balance with a 0.01 gpm resolution, and,
- 3) Charging flow with a 0.01 gpm resolution.
PNP LAR discussion for RP 2.3 identifies two methods, identified in plant TS, that satisfy the first portion of RP 2.3:
- 1) Containment Sump Level required by TS 3.4.15.a, and,
- 2) PCS water inventory balance as required by TS SR 3.4.13.1 Position 2.3 states that methods to consider for meeting the TS requirements are not limited to the list identified by 2.3 (i)-(iii). While PCS water inventory balance is not included by description in the RP 2.3 list, it is identified in TS and therefore satisfies as a 2nd independent and diverse method.
The instrumentation NRC identifies for TS 3.4.15 b, c and d can be associated with the other systems category for the second portion of RP 2.3 which states they do not have to meet the capabilities of RP 2.2.
PNP 2025-047 Page 3 of 6 Precedent:
NRC issued a Safety Evaluation Report (SER) to Calvert Cliffs Nuclear Power Plant (CCNPP)
(Reference 2) approving revisions to TSs to define a new time limit for restoring inoperable reactor coolant system (RCS) leakage detection instrumentation to operable status. The proposed TS changes were consistent with TS Task Force (TSTF)-513, "Revise PWR (Pressurized-Water Reactor) Operability Requirements and Actions for RCS Leakage Instrumentation."
PNPs interpretation of how many leakage detection systems should be in TS to meet RPs 2.2 and 2.3 is supported by discussion on Page 3 of the SER where NRC staff stated:
RG 1.45, Revision 1, "Guidance on Monitoring and Responding to Reactor Coolant System Leakage," was issued in May 2008. RG 1.45, Revision 1, describes methods for implementing GDC 30 requirements that are different from those in RG 1.45, Revision 0, and was developed and issued to support new reactor licensing. Revision 1 allows that having two TS leakage detection methods capable of detecting a one gpm leak within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> provides adequate leakage detection capability from a safety perspective. It recommends that other potential indicators (including the gaseous radiation monitors) be maintained even though they may not have the same detection capability. These indicators, in effect, provide additional defense-in-depth.
Question 2 Section 2.4 of the enclosure to the LAR states that the proposed change will allow the elimination of large break asymmetric dynamic loads in the PCS hot-leg and cold-leg piping from the licensing basis. Given the omission of the crossover-leg main loop piping in the discussion on the LBB scope, clarify whether the LBB methodology is applied to the crossover-leg main loop piping (also called primary loop piping).
Holtec Response to Question 2 Crossover-leg main loop piping is terminology not utilized in the PNP Power Operations Licensing Basis (POLB) Updated Final Safety Analysis Report (UFSAR) (Reference 3), or POLB Technical Specification (TS) Amendment #271 Bases. The PNP PCS piping is comprised of two loops with each loop containing one hot leg pipe from the reactor vessel outlet to the steam generator inlet and two cold leg pipes between the steam generator outlet and the primary (or reactor) coolant pump (PCP or RCP) suction nozzle and between the PCP discharge nozzle and the reactor vessel inlet. This description is consistent with the PNP UFSAR section 4.3.6 on the Primary Coolant Piping. The PCP suction section is evaluated within CEN-367-A (Reference 4) along with all the PCS hot and cold leg loop piping in the PNP.
Question 3 Please clarify the following: (1) how Holtec considered the thermal aging effect of the 60-year operation on the FT properties of the CSS safe ends in the LBB analysis; and (2) whether the FT properties used in the LBB analysis are the saturated properties that can represent the 60-year FT properties and, if not, explanation for why the use of unsaturated FT properties is adequate.
PNP 2025-047 Page 4 of 6 Holtec Response to Question 3 Clarification (1)
PNP would like to clarify use of the term Cast Stainless Steel (CSS) safe ends on page 16 of Section 3.1.2 of the enclosure to the LAR. CSS in this context comes from CEN-367-A safety evaluation (Reference 4) Section 2.1 where it was used to generically describe the cast austenitic stainless steel (or CASS) safe ends in the Combustion Engineering fleet. From Table 2.2 in CEN-367-A, the PNP safe ends at the PCP cold leg suction and discharge are listed as not available. Reference 5 contains the vendor drawings for the transition pieces (safe ends) and shows both transition pieces as being low carbon steel with 304 stainless steel internal cladding. PNP does not have any CASS safe ends in the primary coolant system (PCS).
Reference 6 shows the PCP discharge transition piece attached to the discharge nozzle and the PCP suction transition piece attached to the suction elbow. Reference 7 lists the suction elbow as CASS material (ASTM A-351 Gr. CF8M) and identifies it as part of the Pump Case Assembly. Reference 7 confirms that there is CASS material in the primary piping, however it is at the PCP suction elbows and not the safe ends. There is no additional CASS piping in the PCS hot and cold leg loop piping.
For pump casings and valve bodies fabricated from CASS, the Grimes letter (May 19, 2000)
(Reference 8) stated that screening for susceptibility to thermal aging was not required. For initial license renewal, the suction elbow was considered to be part of the Pump Case Assembly and was assessed as a pump casing component. Therefore, the thermal aging effect of 60-year operation on fracture toughness would not have been required.
Based on the recent information that the PCP suction elbows are CASS material, PNP initiated a corrective action document (Reference 9) to evaluate to what extent the Palisades Aging Management Program (AMP) and Inservice Inspection (ISI) Program should be revised.
Clarification (2)
As stated in Clarification (1), there is CASS material in the PCP suction elbows and not at the safe ends.
As the PCP suction elbow material is confirmed to be CASS, the existing discussion in PNP Life Extension and TLAA contained in Section 3.1.2 of the LAR remains appropriate as-is.
However to reinforce the assessment of thermal aging evaluation on CASS, evaluations reported in Reference 10 have been considered, which demonstrate the tolerance of CASS components to very large flaws, even under extreme loading conditions, and derived from materials aged to simulate a service life of 60 years (520 000 hours0 days <br />0 hours <br />0 weeks <br />0 months <br />) at operating temperatures (e.g., 280-320 °C (536 - 608 °F)). Because the lower-bound fracture toughness of thermally aged CASS is similar to (bounded by) the fracture toughness of submerged arc (SA) welds, the procedures in ASME Code,Section XI, IWB-3640 for SA welds are also applicable to CASS materials (Reference 11).
Several studies and data (Reference 12, Section 3.2) show that the J-R curves for aged Shielded Metal Arc Welding (SMAW) and Gas Tungsten Arc Welding (GTAW) aged type 308L
PNP 2025-047 Page 5 of 6 are above the proposed lower bound in NUREG/CR-6428, Section 1 and 3, for service times corresponding to 54 or 72 EFPY.
As such, since the saturated fracture toughness values are used in the aforementioned evaluations, then the analysis for CASS is inherently conservative and adequately reflects the degraded state after 60 years.
NRC Question 4 In Section 3.1.4 of the enclosure to the LAR, Holtec indicates that the likelihood of primary water stress corrosion cracking (PWSCC) in the PCS main loop piping is eliminated due to the absence of any Alloy 600/82/182 materials of construction in the PCS main loop piping and connection welds.
In contrast, Reference 13 indicates that Palisades has PWSCC-susceptible Alloy 82/182 dissimilar metal welds at the reactor coolant pump (RCP) inlet and outlet nozzles (Reference 13, Section 2.1 and Table 2-1).
Please resolve the apparent inconsistency discussed above regarding the presence of PWSCC-susceptible materials in the Palisades main loop piping. If there is a PWSCC-susceptible material at the RCP inlet or outlet nozzle location, provide the evaluation of the potential impact of the PWSCC-susceptible material on the LBB application.
Holtec Response to Question 4 PNP In-Service Inspection (ISI) Master Program pertaining to the Alloy 600 Program, Section 5.3.5 Reactor Coolant Pumps (Reference 14), states that the PCPs and attachment welds to loop piping do not include Alloy 600 material.
During the 2008 timeframe, PNP Plant staff investigated (Reference 5) the type of material used in the bimetallic welds at the primary coolant pump suction elbow and discharge nozzle transition pieces (safe ends). PNP records showed factory welds between PCP CASS pump suction elbow and discharge nozzle and the pipe transition pieces. The weld material was not identified since these were supplied components and did not directly affect field installation.
PNP obtained the vendors Welding Procedure Specification and transition piece drawings in use at the time of fabrication as documented in Reference 5. The vendor drawing of the transition pieces and the associated welding procedure specified that ASTM A-298, Type E308 was the filler metal used. There was no reference to nickel-alloy weld filler material, therefore, there are no PWSCC susceptible materials used at the PCP suction elbow and outlet nozzle transition pieces.
However, the Reference 5 investigation did note that PNP is the oldest Combustion Engineering PWR and information from other plants indicated that the corresponding welds were made with Alloy 600 type material. PNP cannot speak to the accuracy of Reference 13.
PNP 2025-047 Page 6 of 6 References:
1 Regulatory Guide 1.45, Guidance on Monitoring and Responding to Reactor Coolant System Leakage, Revision 1, dated May 2008 (ADAMS Accession No. ML073200271) 2 NRC Letter to Calvert Cliffs Nuclear Power Plant, Calvert Cliffs Nuclear Power Plant, Unit Nos. 1 and 2 Issuance of Amendment to Facility Operating Licenses RE: Reactor Coolant System Leakage Instrumentation, dated August 24, 2011 (ADAMS Accession No.ML112082543) 3 Palisades Updated Final Safety Analysis Report, Revision 35, ML21125A285 4
Combustion Engineering, Inc., CEN-367-A, Leak-Before-Break Evaluation of Primary Coolant Loop Piping in Combustion Engineering Designed Nuclear Steam Supply Systems, dated February 1991, (ADAMS Accession Number ML20070S390) 5 PNP Condition Report, CR-PLP-2008-02388 6
Palisades Drawing, VEN-M0001-EA, Sheet 77, Revision 76, 35 x 35 x 42 Primary Coolant Pump 7
Palisades Vendor Manual, M0001EA Sheet 1202, Pump Technical Manual Reactor Coolant Pump, Revision 29, Page 102, Materials of Construction 8
Technical Letter NRC000213, License Renewal Issue NO. 98-0030, Thermal Aging Embrittlement of Cast Austenitic Stainless Steel Components, May 19, 2000 (ADAMS Accession No. ML15223A635) 9 PNP Incident Report, IR PAL-07898 10 EPRI TR-106092 Final Report, Evaluation of Thermal Aging Embrittlement for Cast Austenitic Stainless Steel Components in LWR Reactor Coolant Systems, dated September 1997, (ADAMS Accession No. ML003727111) 11 NUREG/CR-7185, Effect of Thermal Aging and Neutron Irradiation on Crack Growth Rate and Fracture Toughness of Cast Stainless Steels and Austenitic Stainless Steel Welds, dated July 2015, (ADAMS Accession No. ML15202A007) 12 Technical Letter Report TLR-RES/DE-2023-14, Revision 0, Assessment of Thermal Aging Embrittlement of Austenitic Stainless Steel Weld Metals, August 13, 2024, (ADAMS Accession No. ML24180A123) 13 Technical Letter Report TLR-RES/DE/REB-2021-14-R1, Probabilistic Leak-Before-Break Evaluations of Pressurized-Water Reactor Piping Systems using the Extremely Low Probability of Rupture Code, April 2022, (ADAMS Accession No. ML22088A006) 14 Program Section No. SEP-ISI-PLP-003, Program Section for Palisades Inservice Inspection Master Program Fifth Interval, ASME Section XI, Division 1, Revision 11